My latest update extends the dual boot of Android and Linux functionality to include booting or installing Linux from a drive connected by a USB port. This means that besides booting Android, you now have the choice to boot Linux from an SD card, from a drive (USB stick or HDD or even another SD card in a card reader) or from NAND.
The drive is prepared exactly in the same way as before when creating an SD card. A root file system (RFS) image can be written to either the drive or its first partition, or the RFS files can be copied to a previously made 'ext4' file system on the disk drive.
As this is an upgrade, first apply the last version of the software (see post below). To apply the upgrade first download the relevant updated boot image:
and overwrite the original 'boot.img' with this one. Then connect your RK3188 device in bootloader mode and for Linux use the Linux upgrade tool and enter:
to flash just the boot partition or for Windows use the 'RKAndroidTool.exe' tool and flashing only the boot image.
When the RK3188 device is booted with an USB connected drive containing a valid RFS then additional boot options will be displayed allowing the booting and installation from the drive.
There is a limitation in that the drive must be the first connected USB device (i.e. /dev/sda) and the RFS must either be on the drive or its first partition (i.e. /dev/sda or /dev/sda1). More complex scenarios should consider modifying the source code.
And the mandatory caveat: Flashing software to a device can cause the device to become 'bricked'. Typically this is due to a specific cause e.g. poor quality USB cable, insufficient power source, manual interruption/intervention, incorrect flashing software etc.. There are several techniques to recover from this situation published on the internet. Whilst this software has been extensively tested on the specific devices without problem, your usage of it is at your own risk.